Key Technology Research Of Laser Radar For Three-dimensional Shape Measurement

Three-dimensional shape measurement technique has been widely used in manufacturing and testing of products components, reconstruction of cultural relics, reverse engineering and other fields. Meanwhile, the large-size, non-contact, high-precision and high-speed three-dimensional shape measurement is the future development trend.At present China widely used the laser tracker to achieve three-dimensional shape measurement. The laser tracker is a contact measurement which is characteristic of needing for a handheld corner cube target ball as cooperative target. Therefore, the materials and size of the measurement object are subject to certain restrictions. With the feature of large measurement range, well environmental adaptability, without cooperation objectives and other characteristics, it makes this article has important theoretical significance and practical value.In the first place, in view of the requirement of high precision 3D profile measurement in large parts, the dissertation proposed a 3D shape measurement method based on the principle of frequency modulation coherent laser radar. By measuring the frequency difference between the transmitter and receiving systems to fulfill laser radar ranging, and using rotary encoder for angle measurement.On the basis of the laser radar three-dimensional shape measurement principle,We conducted a program designed of laser radar three-dimensional shape measurement systems and various subsystems.In the second place, according to the requirement of the three-dimensional shape measurement technology index, the dissertation researched the principle of laser heterodyne detection technology and heterodyne detection efficiency. In the meantime, the scheme of differential frequency interference measurement was given in the dissertation, by measuring the difference between vibrating light and signal light to improve the signal noise ratio of detection system, and solved the weaker problem of the target signal.In addition, the dissertation researched the laser high frequency tuning technique, and selected a fiber grating external cavity semiconductor laser with well continuous tuning, tuning linearity as the light source. Used the piezoelectric effect of PZT to achieve the axial stress of laser. By applying different voltage to the PZT, made it different vibration speeds, and the fiber grating was driven to achieve the wavelength, namely, the frequency of the tuning.What’s more, the dissertation designed a FM coherent laser radar optical system with transmit / receive common optical path. According to Gauss optics theory, the dissertation designed a no focal zoom optical system with three groups beam spreading alignment. At the same time, programmed with ZPL macro language, and drew a zoom curve, made it realize smooth zoom on the machine. On the basis of the radar equation to calculate the echo energy required by the system, and ensure the target return beam had enough echo signals to be detected detector.Last but not least, in order to verify whether the three-dimensional shape measurement system met the demand of technical indicators, the dissertation carried out experiments of autofocus measurements, single-point measurement, repetitive measurement experiment, repeatability measurement to the Harmony EMU CRH380 bullet-shaped front face. The verification results of CCD focusing performance, car point cloud scan results and measurement error distribution results were given. The results fully satisfied the requirements of technical indicators, verified the rationality of the measuring system. The results met the technical requirements, and verify the reasonableness of the measurement system solutions.